In one type of sealing and cutting device an electrically heated resistance wire is passed through two plastic resin film sheets. The heat melts the sheets so that they simultaneously adhere together along a line and are severed along the same line. The wire may be heated either intermittently or constantly and may be temperature controlled. One type of wire sealer is described in U.S. Pat. No. 3,792,770 to Freeman.
Although some types of heated wire sealers may be relatively inexpensive and relatively rapid in operation, they are not able to consistently produce strong liquid-tight leakproof seals. For example, there are likely to be at least a few leaking bags in a group of liquid containing bags sealed by heated wire sealers. In some products the presence of an imperfect or less than consistently perfect seal may be acceptable, for example, in frozen foods packaged in plastic resin film pouches. However, such inferior sealing is not acceptable in other situations. In addition, the seal made by a heated wire has relatively little strength and may easily burst from internal pressure.
At the present time it is possible to seal a few types of plastic film, such as polyvinylchloride (PVC), by means of high-frequency electromagnetic field (radio frequency) sealing devices. However, such high-frequency sealers are not applicable to other types of plastics and specifically they will not seal certain types of polyethylene and polyester films in a liquid-tight seal. There are various applications in which polyvinylchloride film is utilized because a liquid-type seal can be formed using that material; but for other reasons it would be preferable to use other types of plastic resin films. For example, in the use of colostomy bags it is vital that the bag be leakproof. Those colostomy bags which are presently made of polyvinylchloride PVC film present certain disadvantages; for example, the film is not impervious to vapor, which may cause an odor problem. In addition, the PVC film of the bags, in order to be pin-free, that is, free of small pin-size holes, must be relatively thick, in the order of 10 mils. Such PVC film, which is usually made by a casting process, is expensive and conceivably may involve a long-range contamination problem.
It would obviously be preferable to have a disposable colostomy bag made of thinner plastic resin film which is chemically inert, such as polyethylene. However, as explained previously, a seal made by a hot wire, which is a "tear seal," does not provide sufficient strength against bursting from internal pressure. The use of an additional hot wire knife would also not be satisfactory since it would produce only a thin sealing bead not having sufficient strength to prevent bursting from internal pressure. Other examples of products which are presently made of relatively thick polyvinylchloride and which could utilize thinner film of other less expensive or less chemically active materials include other medical products such as blood containers, gloves, disposable foot coverings, laboratory disposable clothing, and other items.